Submersible pump assemblies are widely used in well applications, as for example water wells for use in irrigation or residential systems. Generally, these pump assemblies include an axial discharge pump which is connected to a discharge pipe. The pump motor is carried coaxially below the pump with the motor shaft being coupled in-line to the pump impeller shaft. In such arrangement, the motor shaft carries a substantial axial load due to the weight of the rotor as well as hydraulic loading on the internal components of the pump. In addition, substantial radial loading is experienced by the motor as a result of the torque required to pump the column of water through the discharge pipe an elevation of 100 feet (30.48 m) or more.
The environment in which submersible pumps operate is quite harsh. The pump and motor are submerged in the water, or other well fluid. As such, the motor must be fluid-tight to avoid the well fluid from leaking into the motor housing and causing severe damage. Furthermore, the well casing limits the size of the diameter of the motor.
Because of these operating conditions, the pump motor must be relatively compact in size and capable of producing sufficient usable torque. Furthermore, the reliability of the motor must be significantly good, with a minimum of maintenance.
One of the principal problem areas in any motor is the bearings supporting the rotor shaft. The bearings must be capable of withstanding substantial radial and axial loads, as well as maintaining proper alignment of the rotor relative to the stator. It is also important that the bearings be of relatively low friction to avoid losses in the output power of the motor. In addition, the bearings need to be kept cool so as not to fail prematurely due to the heat generated when the motor is running.
These problems along with the harsh operating conditions and critical design parameters of submersible pump motors make the bearings for such motors of significant importance. One type of bearing assembly commonly found in submersible pump motors is referred to as a Kingsbury-type bearing. Such an assembly employs a stacked arrangement of brass, carbon and steel rings, shoe pads and bushings which provide radial and axial bearing support while also compensating for slight angular misalignment of the bearing housing. This type of bearing assembly, however, is expensive to manufacture and maintain inasmuch as each component must be individually machined to exact tolerances, from expensive material, and carefully assembled in a time-consuming process. Furthermore, failure of any one component may result in the total failure of the entire bearing assembly.
While considerable attention has been directed to the bearing assemblies of submersible pump motors, as yet no solution is known to provide bearings which are inexpensive to manufacture, reliable in operation and able to provide adequate support against axial and radial loadings.